Devulcanization product consisting of scrap rubber, a devulcanization compound, a method for producing same, the reuse thereof in fresh mixtures and the use thereof for producing injection moulded parts

ABSTRACT

A devulcanization product of comminuted scrap rubber of rubber granules, in which the sulfur bridges of the rubber granule surface are broken and activated for a new vulcanization, is produced by treating the rubber granules to swell the rubber structure of the granule surface and by mixing the treated rubber granules with a devulcanization formulation, acting mechanically and chemically reductively on the rubber granules, in a heating and cooling mixer combination. The rubber granules and the devulcanization formulation are heated to a temperature of 105-150° C. and subsequently immediately cooled. A devulcanization compound is prepared by mixing the devulcanization product with vulcanization and binding agents so as to coat the rubber granules uniformly with them The devulcanization compound can also be prepared by coating the swelled rubber granules in layers by admixing vulcanization agents such as accelerators, activators, auxiliary agents, binding agents, oxygen radical donors and scavengers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a devulcanization product of scrap material ofvulcanized rubber of different elastomer basis, devulcanizationcompounds produced therefrom, methods for their manufacture, as well asthe use of the devulcanization product for utilization in freshmixtures, and a devulcanization compound for manufacturing injectionmolded rubber parts.

2. Description of the Related Art

For the devulcanization of scrap rubber differently acting mechanismsand combinations thereof are used such as temperature action (thermaldegradation of the rubber molecule chains), oxygen or ozone action(oxidative degradation), mechanical action, for example, in the form ofstrong shearing, pressing and tearing forces (mechanical degradation)and the action of chemicals (chemically reductive degradation). In eachsituation, energy is supplied in very different forms for cleaving therubber and sulfur bridges. However, in all these known methods, inaddition to cleaving the monosulfide or disulfide crosslinking bridgesof the rubber, an extensive cracking of the C—C bonds of themacromolecules of the rubber occurs also, which inevitably resultstherefore also in a change of the physical and chemical parameters ofthe devulcanization product used as the starting material.

SUMMARY OF THE INVENTION

The object of the invention resides in the manufacture of adevulcanization product as well as of a devulcanization compound ofscrap rubber which are suitable for further processing to new productswithout any value loss worth mentioning.

According to the invention, this object is solved by a devulcanizationproduct of comminuted scrap rubber and a devulcanization compoundproduced thereof in which the comminuted scrap rubber (ground rubber,granules etc.) are devulcanized on their surface in a gentle way and arereactivated for a new vulcanization in this way. While maintaining thelength of the macromolecules of the elastomer basis of the rubber aswell as the properties of the starting material, the poly-sulfur,di-sulfur or mono-sulfur bridges of the rubber matrix of the surface ofthe comminuted scrap rubber are broken and activated for a newvulcanization.

In a further advantageous embodiment of the invention, the comminutedscrap rubber, devulcanized in a gentle way on its surface, isadditionally activated by an oxygen radical donor, for example,peroxides that are conventionally used in the rubber industry. Thisadditionally acting or parallel-occurring activation process, which isdirected to act on the double bonds still present within the rubbermatrix, provides further crosslinking locations for a more intensive newcrosslinking and ensures thus the highest possible phase connection ofthe rubber granule to a fresh mixture or to different binding materialswithin the devulcanization compound. The formation of a weak connectingphase that is poor in acceleration agents and crosslinking agents isthus prevented, and a high physical value level is ensured.

In connection with comminuted scrap rubber, additionally activated withan oxygen radical donor and devulcanized, the scrap rubber is providedalso with a radical scavenger, for example, an aging protecting agent(APA) conventional in the rubber industry. This achieves a delay effectin the vulcanization kinetics.

The devulcanization compound of the present invention is comprised of amixture of devulcanization product according to the invention,vulcanization agent, binding agent as well as optionally technologicalauxiliary agents.

The devulcanization agent is sulfur. The binding agent is in the form ofmaterials which correspond to the scrap rubber basis. For example,gas-phase EPDM is used for EPDM rubber as a binding agent and groundNR/SBR rubber is used for NR/SBR rubber as a binding agent.

For obtaining targeted vulcanization properties and vulcanizationproduct properties, special auxiliary agents for bonding residual air ormoisture are used, for example, CaO and carbon black. For obtaining theflow properties required for the injection molding process, agents forincreasing flowability, for example, “Strukturol EF 44 or EF 66”, or gelforming agents, for example, silicic acid and/or kaolin, are used incombination with plasticizer oil (paraffin oil) or zinc stearate.

Sulfur-crosslinked scrap rubber is used for the invention. The scraprubber can be in the form of scrap rubber produced due totechnical/technological causes but also molded rubber rejects, usedtires recycled in the form of granulate or ground recycled water rubber.

According to the invention, the devulcanization product is produced suchthat the rubber structure of the rubber granule surface of thecomminuted scrap rubber is swelled and the thus pre-treated scrap rubberis then mixed with a devulcanization formulation acting in a mechanical,chemically-reductive way, in a heating and cooling mixer combination andis heated to a temperature up to 105 to maximally 150° C. and issubsequently immediately cooled.

For swelling the rubber structure of the rubber granule surface, talloil, plasticizer oils to be matched to the current polarity of theelastomer basis of the rubber (such as paraffin oil, aromatic,naphthenic oils etc.) and/or organic acids, for example, benzoic acid,are used. This results in a loosening of the rubber structure on therubber granule surface and penetration of the chemicals in thesubsequent method steps to a depth which is within the nano range.

In the temperature range of 105 to 150° C., the devulcanization isrealized by a chemically reductive process by means of thedevulcanization formulation. Heating is realized substantially byprocess-caused frictional heat. Preferably, heat energy is supplied upto reach a removal temperature of up to 135° C. In order to prevent avulcanization process from occurring subsequent to the devulcanization,the chemical-reductive process is controlled such that the comminutedscrap rubber is processed within the active temperature range in a shortperiod of time.

A further process approach is an activation process of rubber doublebonds and sulfur bonds of the rubber matrix on the rubber granulesurface occurring parallel or additionally to the aforementioned methodand carried out by means of activatingly acting chemicals such as oxygenradical donors. For this purpose, after mixing the comminuted scraprubber with the devulcanization formulation, oxygen radical donors areadded to this mixture, and optionally radical scavengers, and mixing iscontinued up to the point of reaching the transfer temperature, andsubsequently the mixture is cooled.

Cryogenically ground rubber (all granule sizes are possible, evenpellets) is preferably employed.

The devulcanization formulation is comprised of a mixture of chemicalsof vulcanization activator, vulcanization accelerator, vulcanizationretarder and/or, optionally, plasticizer oil.

The vulcanization activator or vulcanization accelerator is in the formof chemicals conventionally used in the rubber industry, for example, asa vulcanization accelerator CBS, MBT/DPG, DCBS, thiuram, and as avulcanization activator, for example, zinc oxide in combination withstearic acid or zinc stearate.

The devulcanization retarding agents are in the form of tall oil ororganic acids, for example, benzoic acid.

The plasticizer oils in the case of scrap EPDM is paraffin oil.

The oxygen radical donors are peroxides conventionally used in therubber industry. Recommended is a combination with a radical scavenger,for example, antioxidants, aging protecting agents (APA) etc, but notrequired in all situations.

The manufacture of the devulcanization compound according to theinvention is realized either in a second mixing stage, which is separatefrom the manufacture of the devulcanization product, preferably in thesame device, or in a single-stage process.

In a second processing stage, the devulcanization product is processedto the devulcanization compound. For this purpose, devulcanizationproduct, vulcanization agent, binding agent as well as optionallyauxiliary agents are mixed with one another such that thedevulcanization granule is uniformly enclosed by the additives.

The above mentioned compounds are employed as the vulcanization agent,binding agent, as well as the optional auxiliary agents.

In addition to the two-stage process, a single-stage manufacture of thedevulcanization compound is also possible. For this purpose, bothprocessing stages devulcanization and compound mixing are combined andthe actual reaction processes, i.e., the activation and devulcanization,are moved into the vulcanization process advancing with temperature.According to the invention, the rubber structure of the rubber granulesurface of the comminuted scrap rubber is swelled and, subsequently, thethus pre-treated scrap rubber is coated in layers by mixing withvulcanization accelerator, vulcanization activator, vulcanization agent,auxiliary agent, binding agents, oxygen radical donor and oxygen radicalscavenger.

According to the invention, a method that is gentle with respect to theelastomer structure and is based on a mechanical/chemically reductivemethod or a mechanical/chemically reductive and activating method isused for a defined activation temperature for producing thedevulcanization products according to the invention. The thus produceddevulcanization product is devulcanized and activated on the rubbergranule surface. This process is possible with all sulfur-crosslinkedvulcanization products. In this connection, it is important that thephysical and chemical properties of the rubber starting material remainintact so that admixing of up to 50% into fresh mixture is possiblewithout a loss of the physical parameters worth mentioning (lower than5%) by using mixing technologies conventional in the rubber industry.

The use of a heating and cooling mixer combination ensures a preciselydetermined mechanical/chemically reductive process with defined heatintroduction for process activation in which the rubber matrix isprotected with regard to its molecule chain length against the crackingprocess.

In the heating and cooling mixer a relatively gentle, specially definedmechanical energy introduction into the rubber granule is provided bymeans of the impulse turbulence principle, primarily by frictiongenerated between the particles or upon contact with the stirring tool.In this way, the chemically reductive or activatingly acting chemicalswhich cleave the sulfur bridges are processed into the rubber particlesurface to a penetration depth which can be controlled in a defined wayby the process parameters. Accordingly, they are positionedstrategically for the task of devulcanization.

By means of the cooling mixer arranged downstream, the temperatureeffect can be precisely controlled temporally and, by means of theimmediate quick cooling out of the active temperature range, the onsetof vulcanization and a possible heat lag are prevented.

The chemicals are melted in this process and are thus distributedhomogeneously within the mixture. The temperature which increasescontinuously in the process is generated by the friction of theparticles. The mixture is cooled to its starting temperature only afterthe end of the process; an external heat supply is not required orcontrolled according to a working volume corresponding to the employedmachine. In order to perform the chemically reductive process, atemperature in the range of 105-135° C. is required. The material shouldpass through this active temperature range preferably in 60 to 240seconds. In this connection, the chemicals are transformed into theactive state in which the sulfur chains are cleaved. The S chaincleavage is carried out in that the sulfur bridges are broken upchemically reductively and in that the accelerators with their cleavageproducts actively react with the two sulfur ends of the cleaved bridge.The accelerators are in the form of CBS, MBT/DPG, DCBS, thiuram, etc.During a normal vulcanization they cleave the accelerators, break thedouble bonds of the elastomers, and dock with the sulfur ends of thecleaved products on the free valences of the rubber. During the furthercourse of the vulcanization they provide quickly the sulfur crosslinkingof the macromolecules of the rubber in that they cleave again andquickly allow the sulfur to dock or they participate themselves in thecrosslinking action.

In the process of devulcanization the chemical activation energy of theaccelerator is used only for breaking the S chains. The carbon bridgesof the elastomers are not attacked by this.

The length of the macromolecules of the elastomer basis of the rubberand thus also the properties of the starting material, i.e., of theoriginal mixture, remain intact and provide a safe bonding of highproportions, up to 50%, in the fresh mixture without loss of physicalvalues worth mentioning. This is made possible in that a directcrosslinking between the devulcanization product and the fresh mixturestructure takes place.

It is known that in the vulcanization of fresh mixtures, to whichuntreated ground rubber of vulcanized scrap rubber has been added, afurther or excess vulcanization occurs within the ground particles as aresult of the temperature effect. As a result of this process, sulfurand accelerator are removed from the area immediately adjacent to therubber granule surface and in this way the crosslinking density isgreatly reduced. Accordingly, the physical parameter levels of theentire material are disturbed. The phase connection between the rawrubber/binding agent and the ground particles is not sufficientlyensured. For this reason, in the past it was possible to admix only verysmall amounts of ground rubber of vulcanized scrap rubber to raw rubbermixtures without loss of properties.

The aforementioned process is counteracted by adding peroxide. It givesoff active oxygen radicals. In cooperation with the above mentioneddevulcanization mechanism, the double bonds which are present in therubber matrix of the recycled waste rubber are additionally activatedand, in this way, the crosslinking density relative to the previouslyknown methods is considerably increased and the above described processis prevented.

The chemically reductive process conceivably can be formulated asfollows:

CBS cleavage and reaction:

With regard to the CBS cleavage and reaction, the resulting reactionproducts are a mixed disulfide and a sulfenamide. No oxidation-sensitivemercaptane compounds result which is a great advantage because, until anew vulcanization begins, the active state is maintained by this bondingwhich counteracts an oxygen addition.

The use of tall oil with its high resin acid and fatty acid mixtureproportion and organic acids (for example, organic acids such ascarboxylic acids, benzoic acid) in combination with conventionalplasticizer oils assist in the chemically reductive cleavage process ofthe sulfur bridges. The resin acid proportion acts in the newvulcanization so as to retard the vulcanization kinetics on the rubbergranule surface which is important for the connection to the freshmaterial. It supports phase connection of the rubber granule to thebonding material. Moreover, this oil has a high tackiness which enablesa layered and controlled application of the chemicals (docking) onto therubber granule surface corresponding to the course of the process.Further processing oils (such as paraffin oil, aromatic, naphthenic oilsetc.) which are to be adjusted to the present polarity of the elastomerbasis of the rubber result in a loosening of the rubber structure on therubber granule surface. This enables penetration of the chemicals to adepth which is within the nano range. In this way, the processing oilshave an entraining and distribution function for the active accelerationsubstances and the peroxide.

A further important component for the devulcanization is zinc oxide. ZnOis an activating component for the accelerators, in combination withstearic acid during the course of the devulcanization process and duringthe later vulcanization process.

Stearic acid provides in combination with the accelerators a reactionpotential which takes on a retarding role in the later vulcanization butin the reaction with the zinc white activatingly acting reactionproducts result. Also, stearic acid effects a good filler materialdistribution and during the injection molding process an improvement ofthe flow behavior.

Carbon black, silicic acid, and kaolin are used for improving theflowability as well as for air and moisture adsorption. In this way,microporosity within the vulcanization product which causes a valuelevel decrease, is counteracted or prevented.

A decrease of the new vulcanization intensity is based on oxidativeprocesses (addition of oxygen on the active free bonds). Agingprotecting agents (APA) which counteract the oxidative rubber aging areadvantageous in this process and are automatically provided in theperoxide/APA combination. In the case of cryogenically ground scraprubber, this ground material is protected against oxygen attack by meansof the nitrogen which is still present for an extended period of time,and the active bonding locations resulting from a mechanical grindingprocess are preserved at the same time.

Processing of the devulcanization compound can be realized inconventionally configured injection molding machines for rubber. Theflowability of the material allows feeding via a hopper with stirringelement. The advantage of employing the injection molding processresides particularly in that by means of the screw feed an initialcompression of the material takes place and, in this way, the air whichhas a negative effect, for example, when using the pressing method, isalmost completely removed from the raw material. The remaining amount isthen bonded to carbon black.

The devulcanization compound according to the invention enables for thefirst time a processing of recycled scrap rubber material in aninjection molding process. In this way, molded rubber parts even withcomplicated geometries can be produced in an effective vulcanizationmethod. In contrast to the pressing method which has been employed untilnow in the processing of recycled scrap rubber for manufacturing simpleshaped rubber parts such as sheets for floor coverings and similarparts, in this connection the injection molding process is recommendedbecause already by means of the screw feed the material is initiallycompressed so that the air contents in the devulcanization compound isdrastically reduced which is not the case in the current scrap rubbermaterials and the pressing method and thus leads to air inclusions andquality problems in the finished parts because the scrap rubbermaterials have no or only a minimal flowability and are only compressedwith regard to their structure. The high injection molding pressurewhich is conventionally employed during the injection molding processprovides a further compression of the devulcanization compound accordingto the invention. During the injection molding process thedevulcanization compound material passes within the injection moldingtool the runner distribution system and the very narrow gate (transitionfrom the runner to the actual shaped rubber part). In the area of thegate, as is conventionally done in the injection molding process, thematerial experiences the highest compression, a very high shearingaction and thus heating. The vulcanization process begins suddenly andis completed by the temperature of the tool over the vulcanizationduration. The vulcanization speed of the devulcanization compoundcorresponds to the vulcanization speed of raw rubber. The excellent flowbehavior of the devulcanization compound ensures the exact filling ofthe tool cavities, even for complicated geometries. As a result of thegranular structure of the devulcanization compound, air inclusions inthe injection molding process for producing shaped rubber parts presenta significantly smaller problem in comparison to raw rubber. Theadhesion of the shaped rubber parts of the devulcanization compound inthe tool is reduced in comparison to shaped rubber parts of raw rubberwhich significantly facilitates removal of the shaped rubber parts fromthe tool. For processing the devulcanization compound all injectionmolding machines and injection molding tools which are usually employedfor processing raw rubber can be used.

The injection molding process is carried out at high pressure(conventionally approximately 190 to 210 Mpa). As is conventional in aninjection molding process, the material passes at this pressure thenarrow slot within the gate area, which is slot is matched to thedevulcanization product, and thus undergoes a very great shearingaction. This shearing action, in particular, effects in thedevulcanization compound the excellent cross-linking density forachieving average to high quality specifications of the vulcanizationproduct, comparable to those of fresh mixtures.

DESCRIPTION OF PREFERRED EMBODIMENTS

With the aid of the following embodiments the invention will beexplained in detail.

EXAMPLE 1 Manufacturing Procedure for Devulcanization Product forManufacturing Devulcanization Compound

starting material: EPDM scrap rubber produced due to technologicalcauses comminution, particle size: 0 to 400 μm devulcanizationchemicals: CBS, tall oil, peroxide, radical scavenger employed mixingdevice: heating and cooling mixer combination (Hentschel company) 200 ltotal volume = 160 l useable volume, 65.0 kg batch weight (approximately0.65 filling factor).Devulcanization batches:

Ingredients (theoretical parts) formulation 1 formulation 2 groundrubber (EPDM) 100.00 ground rubber (NR/SBR) 100.00 tall oil 6.00 14.00paraffin oil 5.00 benzoic acid 0.40 accelerator CBS 2.50 2.50 zinc oxide1.50 1.50 stearic acid 0.70 0.70Process Control

no cooling and heating adjusted

the rotational speed is adjusted corresponding to the batch amount(laboratory batch 3000 rpm; production batch 600 rpm).

working steps temp. time remarks 1. introducing ground 55° C.  0 min.rubber, tall oil, paraffin oil, and benzoic acid into the heating mixer2. stirring at highest speed reactivity reduction (600 or 3000 rpm) ofthe rubber granule 3. addition of CBS, ZnO, at 90° C. and stearic acid4. stirring at highest speed devulcanization (600 or 3000 rpm) process5. transferring the mixture 135° C. 16 min. into the cooling mixer 6.cooling off the mixture in DV is stopped the cooling mixer 7. removal45° C.  8 min. total mixing time 24 min.

EXAMPLE 2 Manufacture of the Devulcanization Compound

Ingredients (theoretical parts) formulation 1 formulation 2devulcanization prod. formulation 1 100.00 devulcanization prod.formulation 2 100.00 gas phase EPDM 80% (binding agent) 9.50 carbonblack (binding agent for air) 0.40 NR powder or NR latex (binding agent)6.00 ground sulfur (vulcanization agent) 1.50 2.00 peroxide 98% (oxygenradical donor) 1.00 1.00 aging protecting agent (radical 0.10 0.10scavenger)Process control

no cooling and heating adjusted

if not indicated differently, the rotational speed is adjustedcorresponding to the batch amount (laboratory batch 3000 rpm; productionbatch 600 rpm).

working steps temp. time remarks 1. introducing devulcaniza- appr.  0min. tion product of formula- 55° C. tion 1 or formulation 2 and sulfurinto the heat- ing mixer 2. stirring at highest speed docking of sulfur(600 or 3000 rpm) on the rubber granule surface 3. addition of bindingat 70° C. agents, kaolin, silicic acid and flowability increasing agent4. stirring at medium speed mixing/distributing (600 or 1500 rpm) 5.adding peroxide and at 80° C. APA 6. stirring at medium speedmixing/distributing/ (600 or 1500 rpm) docking 7. transferring themixture at 95° C. 10 min. into the cooling mixer 8. cooling the mixturein the cooling mixer 9. Removal 45° C.  6 min. reaching packagingtemperature total mixing time 16 min.Characterization of the Devulcanization Compounds

The devulcanization compound is similar to the devulcanization productwith respect to visual appearance and behavior. As a result of theflowability which has been maintained, a direct feeding by means ofhoppers into an injection molding apparatus is ensured, providingtechnological advantages.

In the following the physical test results of the EPDM rubberdevulcanization compound, manufactured according to the aboveformulation and method, are illustrated.

physical values (basis EPDM) parameters NOMINAL ACTUAL unit standardhardness 50 +/− 5 50 Shore A DIN 53 505 hardness after +10 +10 Shore ADIN 53 508 aging in air 168 h/70° C. tensile strength minimum 7.0 12.2N/mm² DIN 53 504 tensile strength up to −25% −8.8% N/mm² DIN 53 508after aging in air 168 h/ 70° C. strain at failure minimum 400 700 % DIN53 504 strain at failure up to −35% −28% % DIN 53 508 after aging in air168 h/ 70° C. compression <50 34 % DIN 53 517 set rebound — 40 % DIN 53512 resilience wear — 249 mm² DIN 53 516 lacquer in- slight CD slight CDcontact N 3810 difference permissible discoloration laquer in- no CF noCF corona N 3810 difference permissible formation lacquer in- no WOE noWOE wash-out N 3810 difference permissible effect ozone resist- nocracks no cracks DIN 53509 ance (2 ppm, 25° C., 48 h) cold resistance nocracks no cracks (after 24 h cold storage at −40° C.) insulation re- >10to the 8th >10 to the Ohm N 67019 sistance 8th DIN 53482 tear strengthtest body B 8.5 N/mm DIN 53 507 (6.3 +/− 0.3 mm) PMMA in- no cracks nocracks N 38016 difference permissible PC indifference no cracks nocracks N 38016 permissible remark: test body was vulcanized for 10minutes at 158° C.! ACTUAL values, basis: NR/SBR physical nominal (usedparameters values tires) unit standard hardness — 65 Shore A DIN 53 505(60-90) tensile — 11.00 N/mm² DIN 53 504 strength elongation at — 340 %DIN 53 504 tear compression — 20 % DIN 53 517 set (CS) rebound — 50 %DIN 53 512 resilience wear — 249 mm² DIN 53 516

The EPDM devulcanization compound was subjected to a xenon rapid agingtest according to VW test standard 3930 at the following conditions:

-   -   1. time 1600 hours    -   2. parallel running    -   3. Schwarzstandard temperature 65° C.    -   4. 102:18 rain    -   5. relative humidity 60-80%    -   6. radiation intensity 60 W/m²

Test results:

heating time of the test body 10 minutes

visual appearance of the surface no cracks, carbon black has migrateddistributor: no cracks, carbon black migrated

before after deviation strength (N/mm²) 9.0 7.3 −18.9% reboundresilience (%) 700 570 −18.6% extension (%) 44 42  −4.6% hardness (ShoreA) 49 54 +10.2%

EXAMPLE 3 Preparation of Devulcanization Product for Fresh Mixture

starting material: EPDM scrap rubber produced by technological causescomminution, particle size: 0 to 400 μm devulcanization chemicals: CBS,tall oil, peroxide, radical scavenger employed mixing device: heatingand cooling mixer combination (Hentschel company) 240 l total volume =160 useable volume, 65.0 kg batch weight (appr. 0.65 filling factor)Devulcanization batches:

Ingredients (theoretical parts) formulation 1 formulation 2 groundrubber (EPDM) 100.00 ground rubber (NR/SBR) 100.00 tall oil 6.00 14.00paraffin oil 5.00 benzoic acid 0.40 accelerator CBS 2.50 2.50 zinc oxide1.50 1.50 stearic acid 0.70 0.70 dicumyl peroxide (98%) 1.00 1.00 IPPD0.10 0.10 carnauba wax 2.00 2.00Process control

no cooling and heating adjusted

if not noted otherwise, the rotational speed is adjusted correspondingto the batch amount (laboratory batch 3000 rpm; production batch 600rpm).

working steps temp time remarks 1. feeding ground rubber, at 55° C. 0min. oils, and benzoic acid into the heating mixer 2. stirring athighest speed reactivity reduction (600 or 3000 rpm) of the rubbergranules loosening of the rubber surface 3. addition of CBS, ZnO, at 65°C. SA, kaolin, and stearic acid 4. stirring at highest speed docking(600 or 3000 rpm) 5. then addition of peroxide 80° C. 6. slow stirring(600 rpm) docking 7. then addition of IPPD 90° C. 8. slows stirring (600rpm) docking 9. addition of carnauba wax 100° C. 10. very slow stirringdocking (600 rpm) 11. transfer into the COOL- appr. 10 min. ING MIXER115° C. 12. cooling the mixture in reaction is stopped the cooling mixer13. removal 45° C. 6 total mixing time 16 min.Characterization of the Devulcanization Product

A flowable product results which has a reduced inherent tackiness. Thistackiness of the particles relative to one another results in a typicalrecognition pattern of the devulcanization product which ischaracterized by delayed flow (“crawling”) during pouring processes. Forimproving the flowability and pouring properties of the material, asignificant improvement is achieved with 0.5 to 1.0 part highlydispersed hydrophilic silicic acid and/or kaolin. Moreover, possiblypresent humidity is bonded.

In the following, the results of a test series of EPDM rubberdevulcanization product, manufactured according the above formulationand method, are provided in a direct comparison as a blend component inan EPDM fresh mixture with increasing proportion.

blend variants physical V80/20 (test 16/40 (test 40/60 (test 100 (testparameters mixture/DV) mixture/DV) mixture/DV) mixture-basis) breaking6.76 6.62 5.67 5.73 strength (MPa) strain at 363 378 377 334 failurehardness 82.4 60.6 57.8 60.6 (° Shore A) rebound 34.1 36.2 35.53 31.67resilience (%) rheological tests (180° C.) ML 9.0 9.6 11.0 7.8 TS2 01:1701:21 01:39 01:43 T50 02:11 02:20 02:47 02:52 T90 06:08 06:59 08:1107:13 MH 28.5 25.7 24.2 24.2 RH 0.16 0.12 0.07 0.1 TRH 01:47 01:52 02:0702:28 TPU 159.8 159.8 161.0 159.8 TPL 159.9 180.0 159.4 159.9 test bodyT = HT = 20 min P 95 bar 180° C. D = 6 mm

EXAMPLE 4 Manufacturing Procedure for Single-stage DVC

It is possible to produce the devulcanization compound in a singlestage. In this method, the DV proportion is combined with the DVCproportion in a mixing process and the reaction mechanism of thedevulcanization and activation of the double bond is carried out duringthe course of the vulcanization process of the DVC.

A decisive factor in this connection is a layered application of theindividual mixing components during manufacture.

starting material: EPDM scrap rubber produced by technological causescomminution, particle size: 0 to 400 μm employed mixing device: heatingand cooling mixer combination (Hentschel company) 200 l total volume =160 useable volume, 65.0 kg batch weight (appr. 0.65 filling factor)Batches:

Ingredients (theoretical parts) formulation 1 formulation 2 groundrubber (EPDM) 100.00 ground rubber (NR/SBR) 100.00 tall oil 6.00 14.00paraffin oil 5.00 benzoic acid 0.40 accelerator CBS 2.50 2.50 zinc oxide1.50 1.50 stearic acid 0.70 0.70 gas-phase EPDM 80% 9.5 (binding agent)carbon black (binding agent 0.40 for air) NR powder or NR latex 6.00(binding agent) ground sulfur (vulcanization 1.50 2.00 agent) peroxide98% (oxygen radical 1.00 1.00 donor) aging protecting agent IPPD 0.100.10 (radical scavenger)Process control

working steps temp time remarks 1. feeding ground rubber, appr.  0 min.oils, and benzoic acid 50° C. into the heating mixer 2. stirring athighest speed reactivity reduction (600 or 3000 rpm) of the rubbergranules loosening of the rubber surface 3. addition of acceleratorappr. (CBS), ZnO, and stearic 65° C. acid 4. stirring at highest speeddocking 5. addition of sulfur appr. 70° C. 6. stirring at highest speeddocking (600 or 3000 rpm) 7. addition of kaolin and appr. silicic acid75° C. 8. stirring at highest speed docking (600 rpm or 3000 rpm) 9.addition of binding agent appr. 85° C. 10. slow stirring (1500 ordocking 600 rpm) 11. addition of peroxide and appr. APA 88° C. 12. slowstirring (1500 or docking 600 rpm) 13. transfer into the COOL- appr. 15min. ING MIXER 90° C.- 95° C. 14. cooling the mixture in reaction isstopped the cooling mixer 15. removal appr.  8 45° C. total mixing time23 min.

EXAMPLE 5

On the basis of the devulcanization product of scrap EPDM and raw rubberinjection molded parts are produced according to the followingconditions and compared with one another:

starting material devul- canization starting compound of material scrapEPDM raw rubber manufacture of housings injection molding machine Werner& Pfleiderer GSP 400 VU injection molding tool with six cavities pointrunner diameter 2.5 mm shot weight 2780 g 3150 g screw/cylindertemperature  65° C.  65° C. tool temperature 165° C. 175° C. injectiontime 40 sec. 40 sec. injection pressure 1080 bar 1080 bar vulcanizationduration 350 sec 350 sec evaluation of parts o.k. o.k.List of Abbreviations Used:

APA aging protecting agent CBS (accelerator) N-cyclohexyl-2-mercaptobenzothiozolyl-sulfen- amide DCBS (accelerator) di-cyclohexyl-2-mercaptobenzothiozolyl-sulfen- amide DPG diphenyl guanidine (accelerator) CScompression set EPDM ethylene propylene terpolymer (synthetic rubber)IPPD N-isopropyl-N′-phenyl-p-phenylene diamine (APA, e.g. “4010 NA”) SAsilicic acid MBT 2-mercapto benzthiazol (accelerator) NR natural rubber(natural caoutchouc) SBR styrene-butadiene-rubber (synthetic rubber)thiuram tetramethylene thiuram disulfide (accelerator) vulcanizationretarder e.g. benzoic acidTest results

ML low Mooney (lowest plasticity or tensile stress) TS2 vulcanizationtime after two units of tensile stress increase above minimum T50vulcanization time for 50% of the total tensile stress increase T90vulcanization time for 90% of the total tensile stress increase MH highMooney (highest tensile stress of the rubber)

1. A devulcanization product of comminuted scrap rubber comprised ofrubber granules, in which devulcanization product sulfur bridges of thegranule surface of the rubber granules are broken and activated for anew vulcanization, the devulcanization product produced by, treating therubber granules to swell a rubber structure of the granule surface ofthe rubber granules; admixing a chemically reductive devulcanizationformulation to the rubber granules with the swelled rubber structure;acting mechanically on the rubber granules in a heating and coolingmixer combination and allowing the devulcanization formulation to cleavechemically reductively sulfur bridges of the granule surface, while therubber granules and the devulcanization formulation reach a transfertemperature of 105° C. to 150° C.; and subsequently immediately coolingthe rubber granules and the devulcanization formulation.
 2. Thedevulcanization product according to claim 1, wherein the devulcanizedscrap rubber is additionally activated with an oxygen radical donor. 3.The devulcanization product according to claim 2, wherein the oxygenradical donor is a peroxide.
 4. The devulcanization product according toclaim 2, wherein the devulcanized and additionally activated scraprubber is provided with a radical scavenger.
 5. A devulcanizationcompound comprised of a mixture of the devulcanization product accordingto claim 1, a vulcanization agent, and a binding agent.
 6. Adevulcanization compound according to claim 5, further comprising anauxiliary agent.
 7. A method for producing a devulcanization product ofcomminuted scrap rubber, comprising the steps of: treating the rubbergranules to swell a rubber structure of the granule surface of therubber granules; admixing a chemically reductive devulcanizationformulation to the rubber granules with the swelled rubber structure;acting mechanically on the rubber granules in a heating and coolingmixer combination and allowing the devulcanization formulation to cleavechemically reductively sulfur bridges of the granule surface, while therubber granules and the devulcanization formulation reach a transfertemperature of 105° C. to 150° C.; and subsequently immediately coolingthe rubber granules and the devulcanization formulation.
 8. The methodaccording to claim 7, wherein, in the step of treating, at least onecompound of the group consisting of tall oil, a plasticizer oil, matchedto the present polarity of the elastomer basis of the scrap rubber, andan organic acid is used.
 9. The method according to claim 8, furthercomprising the step of adding an oxygen radical donor to the rubbergranules and the devulcanization formulation before the transfertemperature is reached.
 10. The method according to claim 9, furthercomprising the step of adding a radical scavenger before the transfertemperature is reached.
 11. The method according to claim 9, wherein thedevulcanization formulation is comprised of a mixture of a vulcanizationactivator, a vulcanization accelerator, and a vulcanization retarder.12. The method according to claim 11, wherein the devulcanizationformulation further comprises a plasticizer oil.
 13. The methodaccording to claim 11, wherein the vulcanization accelerator is CBS(N-cyclohexyl-2-mercapto benzothiozolyl-sulfenamide) or MTB/DPG(2-mercapto benzthiazol/diphenyl guanidine) or DCBS(di-cyclohexyl-2-mercapto benzothiozolyl-sulfenamide) or thiuram and thevulcanization activator is zinc stearate or zinc oxide in combinationwith stearic acid.
 14. The method according to claim 11, wherein thevulcanization retarder is tall oil or organic acids.
 15. The methodaccording to claim 10, wherein the oxygen radical donor is a peroxide.16. The method according to claim 15, wherein the peroxide is used incombination with a radical scavenger.
 17. A method for manufacturing adevulcanization compound, comprising the step of: mixing adevulcanization product according to claim 1 with a vulcanization agentand a binding agent so as to coat the devulcanized rubber granulesuniformly with the vulcanization agent and the binding agent.
 18. Themethod according to claim 17, wherein an auxiliary agent is added in thestep of mixing.
 19. A method for preparing a rubber mixture forvulcanization, comprising the steps of: providing a raw rubber mixture;and adding the devulcanization product according to claim 1 to the rawrubber mixture.
 20. A method for manufacturing injection molded rubberparts, comprising the steps of: mixing a devulcanization productaccording to claim 1 with a vulcanization agent and a binding agent soas to coat the devulcanized rubber granules uniformly with thevulcanization agent and the binding agent to produce a devulcanizationcompound; and injection molding the devulcanization compound.